1. Field of the Invention
The present invention relates to a mobile terminal, a wireless relay apparatus, and a mobile communication system, which are suitable in causing a large amount of data to efficiently transmit to, for example, a mobile terminal in a mobile communication system.
2. Description of Related Art
In a mobile communication system, it is important to satisfy the following two different functional requirements: that a mobile terminal (hereinafter suitably referred to as a “mobile station”) is able to efficiently receive data from a base station currently in communication; and that a mobile station switches base stations to maintain data transmission (hereinafter referred to as “handover”). Especially, to implement the handover, it becomes necessary that a mobile station always monitors neighboring base stations.
For example, in Wideband-Code Division Multiple Access (W-CDMA) system that is specified by 3rd generation partnership project (3GPP), as a third generation mobile phone service, a compressed mode is specified as a function for performing monitoring (measurement) of different frequency base stations when performing handover between different frequencies. Specifically, according to the compressed mode, a base station sets gap intervals as shown in FIG. 1, and stops data sending over a dedicated channel (hereinafter referred to as a “dedicated CH”) in the gap intervals, whereas a mobile station switches frequencies by utilizing the time within the gap intervals, and monitors different frequency base stations. Here, the dedicated CH is a transmission channel used for implementing mainly voice transmission and data transmission at a relatively low speed.
The base station end (actually, universal terrestrial radio access network (UTRAN)) makes the determination of the transition to the above-mentioned compressed mode. At that time, the base station end notifies a mobile station of necessary parameters for setting gap intervals at the mobile station in applying the compressed mode.
FIG. 1 shows receiving situation at a mobile station to which this compressed mode is applied. The ordinate of FIG. 1 indicates transmission power, and the abscissa indicates frame transmission time. In W-CDMA communication system, there is specified that transmission rate can be increased temporarily by changing spreading factor, for example. Therefore, the mobile station increases temporarily transmission rate by changing spreading factor, whereas a wireless frame performs processing so as to maintain the same time length as that before changing the spreading factor, thereby creating gap intervals as shown in FIG. 1. When applying the compressed mode, the mobile station sends data by temporarily increasing transmission power as shown in FIG. 1, in order to avoid transmission quality degradation. The time length of the gap intervals is settable at any length of 3 slots, 4 slots, 5 slots, 7 slots, 10 slots, and 14 slots, with respect to 10 ms (=15 slots) of a transmission frame of a physical channel (a dedicated CH), to which the compressed mode is applied.
Further, as shown in FIG. 2, transmission gap pattern PT1 and PT2 are specified in the compressed mode, respectively, and these patterns PT1 and PT2 are alternately repeated the number of transmission gap pattern repetition count (TGPRC). Two gaps of gaps gp1 and gp2 can be created within the patterns PT1 and PT2, respectively. In the patterns PT1 and PT2, the interval lengths of the respective gaps gp1 and gp2, and distances d1 and d2 between the respective gaps gp1 and gp2 are specified in slot units. Gap lengths GL1 and GL2 are specified by the number of frames (10 ms), and are arranged to be as much as the length of 144 frames. The number of the TGPRCs is settable at as much as an infinite number. Accordingly, the mobile station, which is once designated so as to enter the compressed mode by the base station end, comes to keep creating gap intervals for the number of the TGPRCs periodically (infinitely if the TGPRC is set at an infinite number).
Meanwhile, as a method of rapidly improving data transmission rate in a mobile communication system, for example, 3GPP complementarily defines a high speed channel (hereinafter referred to as an “HS-CH”) as an independent channel other than the dedicated CH in FIG. 3A, which is a physical channel to which the compressed mode is originally applied, as shown in FIG. 3. FIG. 3B shows a downlink HS control CH, FIG. 3C shows an HS data CH, and FIG. 3D shows an uplink HS control CH.
Referring to FIG. 3, the HS-CH is a channel over which time sharing data transmission is performed in a shorter cycle (a wireless frame of 2 ms that is called subframe) than a wireless frame (10 ms) of the dedicated CH to which the compressed mode is applied, and it is regarded as a channel that can be shared among a plurality of mobile stations. Under the HS-CH, the reception quality of the HS data CH is monitored on the mobile station end, as a function independent of the monitor function in the compressed mode. It is made possible to realize high speed data transmission service of best effort type by performing, over the uplink HS control CH, feedback transmission of the monitored reception quality information and either of an acknowledge (ACK) and a nonacknowledge (NACK), which are the reception judgment results of the above-mentioned reception data, from a mobile station to a base station. Although the HS-CH is a channel different from the dedicated CH, in a case where the compressed mode is applied to the dedicated CH so as to monitor different frequency base stations, data transmission with a base station becomes impossible even over the HS-CH. Therefore, no assignment of HS data CH is made in the HS-CH intervals corresponding to the gap intervals at which the different frequency base stations are monitored. In order to do such a matter, the base station end, before the gap intervals are created over the dedicated CH, instructs the mobile station end to stop the assignment of HS data, over the downlink HS control CH. On the receipt of this instruction, the mobile station end does not make the assignment of HS data to the HS data CH. Thereafter, on the termination of the gap intervals, namely on the termination of the monitor operation of the different frequency base stations, the base station end sends HS data identification information addressed to a mobile station. The mobile station, on the receipt of the HS data identification information addressed to a local station, monitors the reception quality of the HS data CH, and then performs feedback transmission of the reception quality information and an ACK or an NACK to the base station over the uplink HS control CH.
FIG. 4 shows a flowchart of data transmission control operation on the mobile station end, based on the presence or absence of the application of the above-mentioned compressed mode and the HS-CH assignment.
Referring to FIG. 4, in step S101, a mobile station judges whether the compressed mode is applied from a base station end. The flow proceeds to the processing of step S103 if judged that the compressed mode is not applied, whereas proceeds to the processing of step S102 if judged that the compressed mode is applied. When advanced to the processing step S102, the mobile station creates gap intervals and monitors different frequency base stations, as described above. After the processing of step S102, the flow proceeds to step S103. When advanced to the processing of step S103, the mobile station starts data receiving over the dedicated CH.
Next, in the processing of step S104, the mobile station judges whether there is the HS-CH assignment addressed to a local station, over the downlink HS control CH. The processing is terminated when there is no HS-CH assignment addressed to the local station, whereas the flow proceeds to the processing of step S105 when there is the assignment. When advanced to the processing of step S105, the mobile station starts data receiving over the HS data CH and monitors reception quality. Further, the mobile station, in step S106, sends the base station the reception quality information during the data reception in step S105, and an ACK or an NACK, with use of the uplink HS control CH.
FIG. 5 shows a flowchart of data transmission control operation on a base station, based on the presence or absence of the application of the above-mentioned compressed mode and the data with use of HS-CH.
Referring to FIG. 5, in step S111, the base station judges whether there is the application of the compressed mode to a mobile station currently in communication. The flow proceeds to the processing of step S113 if judged that there is no application of the compressed mode to this mobile station, whereas the flow proceeds to the processing of step S112 if there is the application of the compressed mode. When advanced to the processing of step S112, the base station creates gap intervals. After the processing of step S112, the flow proceeds to step S113. When advanced to the processing of step S113, the base station performs data transmission with use of the dedicated CH of this mobile station.
Next, in the processing of step S114, the base station judges whether there is HS data addressed to a mobile station and it corresponds to the receiving intervals of this mobile station. The processing is terminated if the judged that there is no HS data addressed to the mobile station or it does not correspond to the receiving intervals of this mobile station. On the other hand, if judged that there is the HS data addressed to the mobile station and it corresponds to the receiving intervals of the mobile station, the base station sends, as the processing of step S115, data identification information addressed to the mobile station over the downlink HS control CH, and then receives the HS data with the use of the HS data CH, in step S116.
For example, the following patent document 1 discloses a technique of utilizing the compressed mode in W-CDMA. In this patent document, a base station apparatus creates a transmission schedule so as to send packet data at the time other than the gap intervals at which no data is sent in the compressed mode. In accordance with the technique of this patent document, there is no fear of packet data from being sent at the time other than the time at which no data is sent in the compressed mode. This enables to reduce interference with a communication terminal apparatus and improve throughput.
Japanese Patent Laid-Open No. 2003-153339 (FIG. 1)
However, as described above, in the case where the above-mentioned compressed mode of the dedicated CH is set when performing high speed data transmission over the HS-CH, non-receivable intervals (non-assignable intervals) of HS data CH may occur as shown in FIG. 3. It follows that the downlink HS-CH transmission rate practically degrades. That is, the length of wireless frame of the dedicated CH is as much as 10 ms. In contrast, the length of a subframe of the HS-CH is defined to be only 2 ms. Therefore, when the compressed mode of the dedicated CH is applied at the time of high speed data transmission over the HS-CH, the mobile station may loose a valuable assignment of the HS-CH by the amount of the time corresponding to the above-mentioned gap intervals of the compressed mode. This makes it impossible to transmit data of several subframes thereby to substantially degrade the HS-CH transmission rate. In particular, even in the presence of a mobile station in a favorable reception quality area at which it is unnecessary to execute handover, for example, if the compressed mode is set and the lack of the HS-CH assignment occurs, there is the problem of making it impossible to realize high speed data transmission service that is the aim of the HS-CH.